The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Nuclear plant operators and service companies perform in vessel visual inspections (IVVI) in conjunction with reactor refueling operations to inspect various reactor components for flaws or damage to the reactor vessel and components within the reactor including submerged pipes and bores. For example, a reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has submerged bores that need to be inspected during maintenance routines. Hollow tubular jet pumps having internal bores are positioned within an annulus to provide the required reactor core water flow. During operation of the reactor, components including their weld joints within the reactor can experience inter-granular stress corrosion cracking (IGSCC) and irradiation assisted stress corrosion cracking (IASCC) which can diminish the structural integrity of the reactor components, such as jet pumps, by way of example. It is important to examine the reactor core components and all welds contained therein periodically to determine whether any cracking or failure has occurred.
The ability to accurately and quickly perform the IVVI visual inspections can impact the outage associated with the nuclear reactor and therefore improvements to the accuracy and speed with which visual inspections can be performed can reduce the outage period and save the nuclear plant operator significant expense.
A visual inspection system typically includes one or more camera positioned on a remotely operated vehicle that is positionable within the reactor vessel. Each camera is coupled to a video transmission system that provides an image signal to a remotely located visual display device or storage system. These visual systems are used to inspect the reactor components for flaws or damage and to look for debris that may have accumulated in the reactor. A variety of cameras are used for various tasks including inspections of the outer surface of pipes and inner bores of pipes, apertures and bores. Generally, each visual inspection system (camera, transmission system, and display) is required to meet predefined imaging standards to ensure that the visual inspection is capable of identifying and delineating the necessary specificity in flaw and damage identification. The requirements for IVVI visual inspection systems include visual Testing (VT) standards such as a rigorous EVT-1 standard, by way of example. The EVT-1 standard provides that the imaging system be capable of resolving a 0.0005″ (½ mil) wire on an 18 percent neutral gray background. The EVT-1 standard as well as other known visual inspection standards rely on personal evaluation by an operator to ensure that the imaging system is providing the appropriate image quality to the remote display from which the inspection is performed.
During an IVVI inspection, the imaging system is evaluated by providing an appropriately sized wire on an appropriate gray background with predetermined and controlled lighting. The operator views the received image and determines the adequacy of the quality of the visual inspection system before proceeding with the IVVI inspection. As such, the assessment of the image quality, and therefore, the IVVI inspection of the nuclear reactor for flaws and damage, are entirely subjective and are therefore inconsistent over time and by operator. Any inconsistencies can result in the failure of the visual inspection system in providing an image for viewing in which the operator can identify a potential flaw or damage which can result in failure to identify such, or can require re-inspection, and therefore added time and costs for the IVVI inspection.